1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and devices and, more particularly, to mechanisms and techniques for providing biasing forces to various parts of an apparatus for sealing a well.
2. Discussion of the Background
One apparatus for sealing a well is a blowout preventer (BOP). BOP is a safety mechanism that is used at a wellhead of an oil or gas well. The BOP may be used for offshore drilling (surface or subsea) and also for land-based drilling. The BOP is configured to shut the flow from the well when certain events occur. One such event may be the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure exceeds the pressure generated by the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent it, the well and/or the associated equipment may be damaged.
Thus, it is desirable that the BOP does not malfunction. One case when the BOP may malfunction is when parts of the BOP are worn and thus, they fail to properly maintain the pressure in the well. The wear process may occur, for example, at the packers attached to the ram blocks of the BOP. When a blowout occurs and the packers are worn, the BOP may fail to properly seal the well, resulting in, for example, damage to the BOP and/or other equipment attached to the well. Therefore, the wear state of the parts of the BOP should be monitored and the worn parts should be replaced to prevent the failure of the BOP. Other events that may damage the integrity of the well and/or associated equipment are possible as would be appreciated by those skilled in the art.
The BOP may be installed on top of the well to seal the well in case that one of the above events is threatening the integrity of the well. The BOP is conventionally implemented as a valve to prevent the release of pressure either in the annular space between the casing and the drill pipe or in the open hole (i.e., hole with no drill pipe) during drilling or completion operations. However, in order to seal the well for a certain time, the elements of the BOP that achieve the seal should be able to maintain the sealing despite the normal wearing process that occurs due to repeated closing and opening of the BOP sealing elements.
One way to maintain the sealing of the BOP is to regularly inspect its components and change those that are worn. However, this process is time consuming, as the components of the BOP are difficult to access and/or inspect as they are undersea or in remote areas, and also expensive, as the operation of the rig has to be stopped.
FIG. 1 shows a well 10. A wellhead 12 of the well 10 may be fixed to the seabed 14. The BOP 16 is secured to the wellhead 12. FIG. 1 shows, for clarity, the BOP 16 detached from the wellhead 12. However, the BOP 16 is attached to the wellhead 12 or other part of the well. A pipe 18 is shown traversing the BOP 16 and entering the well 10. The BOP 16 may have two ram blocks 20 attached to corresponding pistons 22. The pistons 22 move integrally with the ram blocks 20 along directions A and B to close the well 10.
A cut view of the BOP 16 that shows the ram blocks 20 is shown in FIG. 2. The ram blocks 20 are shown moving inside a cavity 24. The cavity 24 may be bordered by a top seat 26 and a wear plate 28. The part of cavity 24 bordered by the top seat 26 and the wear plate 28 may contact the ram blocks 20 tighter than the remainder of the cavity 24. The ram blocks 20 may include a packer 30 (which may be an elastomer) and a top seal 31, which seals the well 10 when the ram blocks 20 are closed.
Given this arrangement of the BOP 16 and the fact that the weight of the ram block 20 may be substantial (in one application the weight may be about 200 Kg), the friction between the ram block 20 and a lower surface of the cavity 24 is high, producing a substantial amount of wear on the BOP 16, consequently deteriorating the sealing performance of the BOP 16. The noted wear has been observed, for example, in the wear plate 28, the upper seat 26, the cavity 24, etc. As a result of the wearing process, the affected elements of the BOP 16 have to be often changed/inspected such that the sealing capacity of the BOP is maintained. However, the maintenance and cost to replace these elements is high and thus, undesirable.
Accordingly, it would be desirable to provide systems and methods that maintain the sealing of the well with a low cost, low downtime operation, and also avoid the above noted shortcomings.